1. Field of Invention
The present invention relates generally to optical systems, and more specifically to optical systems used in video and other projection systems.
2. Discussion of Background
The functionality of a video projector (illustrated containing a commercially available prism assembly) is explained with reference to FIG. 1A. As shown, white light is generated by the light source. The light is collected, homogenized and formed into the proper shape by the condenser. UV and IR components are eliminated by filters. The white light then enters the prism assembly where it is polarized and broken into red, green and blue beams. (Hence a “three channel” type prism assembly.) These beams then follow different paths within the prism assembly such that each beam is directed to a specific reflective microdisplay. The microdisplay that interacts with the green beam contains the green content of the full color video image. It is similar for the blue and red microdisplays. On a pixel by pixel basis, the microdisplays modulate and then reflect the colored light beams. The prism assembly then recombines the modulated beams into a white light beam that contains a full color video image. The resultant white light beam then exits the prism assembly and enters the projection lens. Finally, the image-containing beam is projected onto (in this case) the rear of a screen.
Some desirable properties of a prism assembly are that it produce an image in which the brightness and color are spatially uniform and meet other required optical properties including those for brightness, color gamut and contrast ratio. It is equally important that the prism assembly be manufacturable. That is, that the prism assembly be producible in high volume with good yield and at a high quality level. Finally, and of equal importance, is that the prism assembly meet cost targets. Targets that, for consumer products, are inevitably very challenging.
The configurations of several prism assemblies have been discussed in the technical literature. Included are the following:                Digital Reflection's Star Prism        Philip's Trichroic Prism        IBM's X-Prism+3 PBS        S-Vision/Aurora System's Off-Axis Prism        Digital Reflection's MG Prism        ColorLink's Color Quad Prism        Unaxis'Color Corner Prism        ITRI's Prism        Primax's X-Prism        
However, none of these prism assemblies fully meet all of the criteria discussed above. For this reason, LightMaster Systems has invented and developed a prism assembly according to the present invention that more fully meets these criteria. Details of the prism assembly according to the present invention are provided herein below.